Optical waveguide device module

ABSTRACT

An optical waveguide device module is provided, wherein a control electrode includes a signal electrode and ground electrodes disposed to sandwich the signal electrode, a connection substrate is provided with a signal line and ground lines disposed to sandwich the signal line, the distance W 1  between the ground electrodes in the input end or the output end of the control electrode is larger than the distance W 2  between the ground lines on the optical waveguide device side of the connection substrate, the control electrode has a portion of which the distance between the ground electrodes is smaller than the distance W 2  in a portion away from the input end or the output end thereof, and interconnections of which the distance W between ground interconnections connecting the optical waveguide device and the connection substrate is at least smaller than the distance W 1.

BACKGROUND OF THE INVENTION

Priority is claimed to Japan Pat. App. Ser. No. 2010-076053, filed Mar.29, 2010, hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to an optical waveguide device module, andspecifically to an optical waveguide device module in which an opticalwaveguide device and a connection substrate are accommodated within acasing.

DESCRIPTION OF RELATED ART

In the optical measurement technical field or the optical communicationtechnical field, optical waveguide devices are widely used in which anoptical waveguide is formed in a substrate, having an electro-opticeffect, such as an optical modulator or an optical switch. Usually,these optical waveguide devices are accommodated within an airtightcasing, and form an optical waveguide device module.

As disclosed in Japanese Unexamined Patent Application Publication No.2003-233043, a relay substrate for electrically connecting an input linefrom the outside to a control electrode of the optical waveguide device,or a termination substrate, electrically connected to the output side ofthe control electrode of the optical waveguide device, for absorbing anoutput signal or leading out to the outside of the module isaccommodated within a casing of the optical waveguide device module.

Usually, in order to improve the frequency characteristic by reducingdiscontinuity of the connection portions, as shown in FIG. 1, theelectrode sizes or the distances between ground electrodes (GND) of amodulation substrate and a relay substrate which are included in theoptical waveguide device are designed so as to be equal to each other.In addition, the same is true of the connection of the terminationsubstrate and the modulation substrate. In this manner, when the sizesor the distances of the electrodes of the modulation substrate and theconnection substrate are matched to each other, it is required toprepare the connection substrate only for kinds of optical waveguidedevices, which results in an increase in the manufacturing cost.

Progress is being made in terms of achieving a higher frequency (widerbandwidth) in the optical waveguide devices, and materials, which have alower dielectric constant than that of a substrate (modulationsubstrate), such as alumina, included in the optical waveguide device,have come to be used in the relay substrate shown in FIGS. 2A and 2B. Inaddition, since the frequency characteristic is prevented from beingdeteriorated by a substrate mode and the like, the sizes of theconnection portions such as the relay substrate also become small. Forthis reason, as in the related art, when the distances of GNDs are madeequal to each other, the width of a signal electrode of the opticalwaveguide device becomes small. Therefore, since the widths of thesignal lines of a substrate or a semiconductor substrate, such asLiNbO₃, having an electro-optic effect and the relay substrate aredifferent from each other, discontinuity of the connection portionsoccurs and thus the electrical characteristics are caused to bedeteriorated. In addition, when the width of the signal lines or thedistance of the ground (GND) lines are rapidly changed between the inputside and the output side of the relay substrate, impedance mismatchingeasily occurs, and the deterioration of the electrical characteristicsbecomes even more remarkable.

Further, in order to match the input line from the outside and impedanceof the relay substrate and the optical waveguide device, as shown inFIG. 2B (corresponding to an enlarged view of the portion of sign X inFIG. 2A), when the width of the signal electrode S1 of the opticalwaveguide device and the width of the signal line S2 of the relaysubstrate are made different from each other, and the distance W1between the ground electrodes of the optical waveguide device and thedistance W2 between the ground lines of the relay substrate are madedifferent from each other, the electric field intensities of the signalportion and the ground portion are different from each other in therelay substrate and the optical waveguide device, discontinuity in theelectrical connection occurs, and deterioration of the electricalcharacteristics results. Meanwhile, reference numerals 1 and 2 denoteinterconnections that electrically connect the optical waveguide deviceand the relay substrate.

SUMMARY OF THE INVENTION

The invention is to solve the above-mentioned problems, and to providean optical waveguide device module in which discontinuity in theelectrical connection of the optical waveguide device and the connectionsubstrate (relay substrate or termination substrate) is reduced anddeterioration of the electrical characteristics is prevented.Furthermore, it is to provide an optical waveguide device module capableof using a common connection substrate with respect to a different typeof optical waveguide device and lowering the manufacturing costs.

In order to solve the above-mentioned problem, there is provided anoptical waveguide device module including: an optical waveguide deviceincluding a substrate having an electro-optic effect, an opticalwaveguide formed in the substrate, and a control electrode forcontrolling light waves propagated through the optical waveguide; aconnection substrate including an interconnection, provided to theoutside of the optical waveguide device, which is electrically connectedto the control electrode; and a casing that accommodates the opticalwaveguide device and the connection substrate therein, wherein thecontrol electrode includes a signal electrode and ground electrodesdisposed so as to sandwich the signal electrode, the connectionsubstrate is provided with a signal line and ground lines disposed so asto sandwich the signal line, the distance W1 between the groundelectrodes in the input end or the output end of the control electrodeis larger than the distance W2 between the ground lines on the opticalwaveguide device side of the connection substrate, the control electrodehas a portion of which the distance between the ground electrodes issmaller than the distance. W2 in a portion away from the input end orthe output end thereof, and the optical waveguide device module includesinterconnections of which the distance W between ground interconnectionsthat connect the optical waveguide device and the connection substrateis at least smaller than the distance W1.

In the above-mentioned optical waveguide device module, a connectionposition of the end on the optical waveguide device side of the groundinterconnection is connected to a portion smaller than the distance W2.

In the above-mentioned optical waveguide device module, the opticalwaveguide device module includes other interconnections, which aredisposed so as to sandwich the ground interconnection that connects theoptical waveguide device and the connection substrate, and of which theinterconnection distance is larger than the distance W1.

In the above-mentioned optical waveguide device module, the width of thesignal electrode in the input end or the output end and the width of thesignal line on the optical waveguide device side are different from eachother in size.

In the above-mentioned optical waveguide device module, the dielectricconstant of the connection substrate is lower than the dielectricconstant of the substrate included in the optical waveguide device.

In the above-mentioned optical waveguide device module, theinterconnection that connects the optical waveguide device and theconnection substrate is formed by wire bonding.

According to the above-mentioned configuration, the distance W1 betweenthe ground electrodes in the input end or the output end of the controlelectrode of the optical waveguide device is larger than the distance W2between the ground lines on the optical waveguide device side of theconnection substrate, the control electrode has a portion of which thedistance between the ground electrodes is smaller than the distance W2in a portion away from the input end or the output end thereof, and theoptical waveguide device module includes at least interconnections ofwhich the distance W between ground interconnections that connect theoptical waveguide device and the connection substrate is smaller thanthe distance W1. Thereby, it is possible to restrict the electric fieldintensities of the signal portion and the ground portion from differingbetween the connection substrate and the optical waveguide device, toreduce the electrically, discontinuous portions in the connectionportions of the two, and to prevent the electrical characteristics suchas a high frequency characteristic from being deteriorated. Furthermore,even with respect to an optical waveguide device having electrodes withdifferent sizes or distances, it is possible to proceed appropriately byusing a common connection substrate, thereby allowing the manufacturingcosts to be lowered.

According to the above-mentioned configuration, since a connectionposition of the end on the optical waveguide device side of the groundinterconnection is connected to a portion smaller than the distance W2,it is possible to more continuously change the electric field intensityfrom the connection substrate side to the optical waveguide device side,thereby allowing deterioration of the electrical characteristics to besuppressed.

According to the above-mentioned configuration, since the opticalwaveguide device module includes other interconnections, which aredisposed so as to sandwich the ground interconnection that connects theoptical waveguide device and the connection substrate, and of which theinterconnection distance is larger than the distance W1, it is possibleto more reliably perform the electrical connection of the groundportions.

According to the above-mentioned configuration, the width of the signalelectrode in the input end or the output end of the control electrodeand the width of the signal line on the optical waveguide device sideare different from each other in size. Therefore, electricaldiscontinuity due to the connection portions usually occurs, but thedistance W between the ground interconnections that connect the opticalwaveguide device and the connection substrate is set to be smaller thanthe distance W1, whereby it is possible to suppress discontinuity of theelectrical strength, and to prevent the electrical characteristics frombeing deteriorated.

According to the above-mentioned configuration, the dielectric constantof the connection substrate is lower than the dielectric constant of thesubstrate included in the optical waveguide device. Therefore, whenimpedance matching is performed, the width of the signal electrode orthe distance between the ground electrodes in the connection portions isusually set to values different from those of the signal line or theground line of the connection substrate, but in the invention,discontinuity in the connection portions can be suppressed.

According to the above-mentioned configuration, since theinterconnection that connects the optical waveguide device and theconnection substrate is formed by wire bonding, the distance W betweenthe ground interconnections can be easily set to be smaller than thedistance W1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining a conventional optical waveguidedevice module.

FIGS. 2A and 2B are diagrams for explaining an electrode structure andthe like when a material having a lower dielectric constant than that ofa substrate of an optical waveguide device is used in a relay substrate.

FIG. 3 is a diagram for explaining an interconnection state between anoptical waveguide device and a connection substrate used in an opticalwaveguide device module according to the invention.

FIG. 4 is a graph illustrating a comparison result of an opticalfrequency response between the invention and the prior art.

FIG. 5 is a diagram illustrating an interconnection example when thedistance between ground electrodes of the optical waveguide device inthe optical waveguide device module according to the invention israpidly changed.

FIG. 6 is a diagram illustrating an interconnection example when thewidth of a signal electrode of the optical waveguide device and thewidth of a signal line of the connection substrate in the opticalwaveguide device module according to the invention are equal to eachother.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an optical waveguide device module according to theinvention will be described in detail using a preferred example. Asshown in FIG. 3, the optical waveguide device module according to theinvention includes: an optical waveguide device including a substratehaving an electro-optic effect, an optical waveguide formed in thesubstrate, and a control electrode for controlling light wavespropagated through the optical waveguide; a connection substrateincluding an interconnection, provided to the outside of the opticalwaveguide device, which is electrically connected to the controlelectrode; and a casing that accommodates the optical waveguide deviceand the connection substrate therein, wherein the control electrodeincludes a signal electrode and ground electrodes disposed so as tosandwich the signal electrode, the connection substrate is provided witha signal line and ground lines disposed so as to sandwich the signalline, the distance W1 between the ground electrodes in the input end orthe output end of the control electrode is larger than the distance W2between the ground lines on the optical waveguide device side of theconnection substrate, the control electrode has a portion of which thedistance between the ground electrodes is smaller than the distance W2in a portion away from the input end or the output end thereof, and theoptical waveguide device module includes interconnections of which thedistance W between ground interconnections 3 that connect the opticalwaveguide device and the connection substrate is at least smaller thanthe distance W1.

As a substrate having an electro-optic effect, particularly, any singlecrystal of LiNbO₃, LiTaO₅ or PLZT (lead lanthanum zirconate titanate)can be properly used. Particularly, LiNbO₃ and LiTaO₅, which are oftenused in optical modulators, are preferably used. In addition, theoptical waveguide formed in the substrate is formed by thermallydiffusing, for example, high-refractive-index materials such as titanium(Ti) on a LiNbO₃ substrate (LN substrate). In addition, the opticalwaveguide can also be formed as a ridge optical waveguide by forming agroove in the lateral face of the optical waveguide or forming theoptical waveguide portion thicker than the other substrate portion.

The control electrode includes the signal electrode and the groundelectrodes, forms a Ti/Au electrode pattern on the surface of thesubstrate and can be formed by a gold plating method or the like.Further, a buffer layer such as a dielectric of SiO₂ can be alsoprovided, as necessary, on the surface of the substrate after theformation of the optical waveguide.

The “connection substrate” in the invention means a relay substrate thatconnects an input terminal to which an electrical signal is input fromthe outside and a signal input section of the optical waveguide device,a terminator that absorbs the electrical signal by a resistor or thelike, connected to the output end of the signal electrode of the opticalwaveguide device, in order to suppress reflection of the electricalsignal, or a termination substrate that connects the output end of thesignal electrode of the optical waveguide device and an output terminalthereof, and the like. As a substrate material of the connectionsubstrate, a material having a lower dielectric constant than that ofthe substrate material of the optical waveguide device, for example,alumina or a semiconductor material is used. This is to contribute tothe wider bandwidth of the optical waveguide device.

As an interconnection that connects the optical waveguide device and theconnection substrate, a gold wire or a wide-width gold ribbon can beused. In particular, a method of performing wire bonding of a gold wireis preferable as a method of wiring the two. In addition, theinterconnection is not limited to one, and the vicinity of the sameplace may be connected by a plurality of gold wires.

As shown in FIG. 3, the distance W1 between the ground electrodes of theoptical waveguide device and the distance W2 between the ground lines ofthe connection substrate are different from each other. In particular,when the distance W1 is larger than the distance W2, the distance Wbetween interconnections 3 that electrically connect the connectionsubstrate and the optical waveguide device is made smaller than thedistance W1. Thereby, the difference between the electric fieldintensity between the signal electrode and the ground electrode of theoptical waveguide device and the electric field intensity between thesignal line and the ground line of the connection substrate becomessmall and thus the optical frequency response is improved.

In addition, the connection positions of the ground interconnections 3at the ends of the optical waveguide device side can also be connectedto the portions smaller than the distance W2. In such a case, since achange in the electric field intensity from the connection substrateside to the optical waveguide device side can be made more continuously,deterioration of the electrical characteristics can be furthersuppressed.

As shown in FIG. 3, it is also possible to provide otherinterconnections 2, having an interconnection distance larger than thedistance W1, which are disposed so as to sandwich groundinterconnections that connect the optical waveguide device and theconnection substrate. Such interconnections 2 are the same asconventional interconnections 2 as shown in FIGS. 2A and 2B. It ispossible to more reliably perform electrical connection of the groundportions by connecting the ground electrodes by the interconnections 2and 3.

In FIG. 3, since the width of the signal electrode in the input end orthe output end of the control electrode and the width of the signal lineof the optical waveguide device side are different from each other insize, electrical discontinuity due to the connections usually occurs.However, as in the invention, the distance W between the groundinterconnections that connect the optical waveguide device and theconnection substrate is set to be smaller than the distance W1, wherebyit is possible to suppress discontinuity of the electrical strength, andto prevent the electrical characteristics from being deteriorated.

The width of the signal line of the connection substrate is in a rangeof 0.1 mm to 1 mm, more preferably 0.2 mm to 0.5 mm. In addition, thethickness of the connection substrate is in a range of 0.1 mm to 1 mm,more preferably 0.2 mm to 0.5 mm.

The width between the ends of the signal electrode included in theoptical waveguide device is in a range of 0.03 mm to 0.5 mm, morepreferably 0.05 mm to 0.25 mm.

As shown in FIG. 5, even when the width between the ground electrodesrapidly changes, it is possible to lessen rapid changes in the electricfield intensity by providing the interconnection 3 as in the invention.

In addition, as shown in FIG. 6, the width of the signal line of theconnection substrate and the width of the signal electrode of theoptical waveguide device are configured to be the same, and connectionis performed using a plurality of gold wires or a wide-width goldribbon, whereby it is possible to improve the high frequencycharacteristic. In such a case, since there is an increasingpossibility, from the relation to impedance matching, that the distancebetween the ground lines and the distance between the ground electrodeswill be different from each other, the method of connecting theinterconnections as in the invention can be applied more effectively.

FIG. 4 shows a result obtained by comparing the optical frequencyresponse of the optical waveguide device module according to theinvention shown in FIG. 3 with the optical frequency response in theprior art shown in FIGS. 2A and 2B. From the graph of FIG. 4, it can beeasily understood that the characteristics of the optical waveguidedevice module according to the invention are improved over the entirefrequency band.

As described above, according to the invention, it is possible toprovide an optical waveguide device module in which discontinuity in theelectrical connection of the optical waveguide device and the connectionsubstrate is reduced and deterioration of the electrical characteristicsis prevented. Furthermore, it is also possible to provide an opticalwaveguide device module capable of using a common connection substratewith respect to different types of optical waveguide device and loweringthe manufacturing costs.

What is claimed is:
 1. An optical waveguide device module comprising: anoptical waveguide device including a substrate having an electro-opticeffect, an optical waveguide formed in the substrate, and a controlelectrode for controlling light waves propagated through the opticalwaveguide; a connection substrate including an interconnection, providedto the outside of the optical waveguide device, which is electricallyconnected to the control electrode; and a casing that accommodates theoptical waveguide device and the connection substrate therein, whereinthe control electrode includes a signal electrode and ground electrodesdisposed so as to sandwich the signal electrode, the connectionsubstrate is provided with a signal line and ground lines disposed so asto sandwich the signal line, a distance W1 between inner edges of theground electrodes closest to the signal electrode, measured at an inputend or output end of the control electrode, is larger than a distance W2between inner edges of the ground lines closest to the signal line onthe optical waveguide device side of the connection substrate, thecontrol electrode has a portion in which the distance between the groundelectrodes is smaller than the distance W2 in a portion away from theinput end or the output end thereof, and the optical waveguide devicemodule includes ground interconnections that connect the opticalwaveguide device and the ground lines of the connection substrate,wherein a distance W between the ground interconnections measured at thepoint where the ground interconnections connect with the ground lines issmaller than the distance W1.
 2. The optical waveguide device moduleaccording to claim 1, wherein the optical waveguide device moduleincludes other interconnections, which are disposed so as to sandwichthe ground interconnections that connect the optical waveguide deviceand the connection substrate, and of which the interconnection distanceis larger than the distance W1.
 3. The optical waveguide device moduleaccording to claim 1, wherein the width of the signal electrode in theinput end or the output end and the width of the signal line on theoptical waveguide device side are different from each other in size. 4.The optical waveguide device module according to claim 1, wherein thedielectric constant of the connection substrate is lower than thedielectric constant of the substrate included in the optical waveguidedevice.
 5. The optical waveguide device module according to claim 1,wherein the interconnection that connects the optical waveguide deviceand the connection substrate is formed by wire bonding.
 6. The opticalwaveguide device module according to claim 2, wherein the width of thesignal electrode in the input end or the output end and the width of thesignal line on the optical waveguide device side are different from eachother in size.
 7. The optical waveguide device module according to claim2, wherein the dielectric constant of the connection substrate is lowerthan the dielectric constant of the substrate included in the opticalwaveguide device.
 8. The optical waveguide device module according toclaim 3, wherein the dielectric constant of the connection substrate islower than the dielectric constant of the substrate included in theoptical waveguide device.
 9. The optical waveguide device moduleaccording to claim 2, wherein the interconnection that connects theoptical waveguide device and the connection substrate is formed by wirebonding.
 10. The optical waveguide device module according to claim 3,wherein the interconnection that connects the optical waveguide deviceand the connection substrate is formed by wire bonding.
 11. The opticalwaveguide device module according to claim 4, wherein theinterconnection that connects the optical waveguide device and theconnection substrate is formed by wire bonding.